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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L (LG8) 🢒 Detonation/Spark Knock

Detonation/Spark Knock

Inspection/Test

Action

DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening.

Preliminary
    •  Refer to Intermittent Conditions before starting.
    •  Search for bulletins.

Fuel System
    •  Test for low fuel pressure. Refer to Fuel System Pressure Test .
    •  Inspect for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    •  Inspect any items which may cause an engine to run rich (long term fuel trim is significantly in the negative range). Refer to DTC P0172 Fuel Trim System Rich .
    •  Inspect any items which may cause an engine to run lean (long term fuel trim is significantly in the positive range). Refer to DTC P0171 Fuel Trim System Lean .

Ignition System

Inspect the spark plugs for proper heat range and reach. Refer to Spark Plug Usage .

    • Inspect for proper ignition voltage output using the following steps:
        1.  Attach the J 26792 spark tester to engine ground.
        2.  Connect the spark plug end of the spark plug wire to the J 26792 spark tester; leave the other end of the spark plug wire connected to the coil being tested.
        3.  Connect the spark plug end of the companion spark plug wire to ground.

The companion spark plug wire is the wire attached to the corresponding coil tower.

        4.  Crank the engine while observing the J 26792 spark tester; a spark should be observed.
        5.  Repeat the above steps for each coil.
    •  If spark is not present at the coils, inspect for the following conditions:
       -  Coils--Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Resistance
5000-8000ohms (5K-8Kohms)

       -  Spark Plug wires--signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
600ohms per foot (1 968ohms per meter).

    Important: :  Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition voltage will arc to ground when a secondary component is faulty.

       -  Defective ignition module.
       -  Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring.
    •  Remove spark plugs and inspect for the following conditions:
       -  Fouled plugs
       -  Cracks
       -  Wear
       -  Improper gap
       -  Burned or damaged electrodes
       -  Improper heat range or reach

Engine Cooling System

Inspect for obvious overheating conditions:

    •  Low engine coolant
    •  Restricted air flow to radiator, or restricted water flow through radiator
    •  Inoperative electric cooling fan circuits
    •  Correct coolant solution should be a 50/50 mix--Refer to Coolant Description in Engine Cooling.

Engine Mechanical
    • Excessive oil in combustion chamber or leaking valve seals--Refer to Base Engine Misfire Diagnosis in Engine Mechanical.
    •  Low cylinder compression--Refer to Engine Noise Diagnosis in Engine Mechanical.
    •  Combustion chambers for excessive carbon buildup--Clean using Top engine cleaner. Follow instructions on can.
    • Inspect for the following incorrect basic engine parts:
       -  Camshaft
       -  Cylinder heads
       -  Pistons, etc.
    • For more diagnostic aids refer to Engine Compression Test in Engine Mechanical.

Additional
    •  Inspect for proper EGR system Operation. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .
    •  Inspect the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive.
    •  Test TCC operation. TCC applying too soon can cause the engine to spark knock. Refer to Torque Converter Diagnosis in Automatic Transaxle.
    •  If scan tool readings are normal and there are no engine mechanical faults, fill the fuel tank with a known quality gasoline that has a minimum octane reading of 87 and re-evaluate vehicle performance.